I dont see this route happening..
If they are to offer fares such as 1 cent each way, I think that it WILL become a reality!
If we look at Alicante-Madrid (both airports are FR base) where Ryanair launched some time ago, the timings are extremely early and extremely late. Ie not perfect timings for the business traveller to make a day trip. Reading between the lines it would lead to think that AENA only offered Ryanair preferential fees on timings that dont allow Ryanair to get at the core customer base of Iberia, I may be wrong.
But if that is so, flying El Prat-Madrid would probably mean that Ryanair does an Alicante Madrid style operation, or be faced with high fees, El Prat would be unlikely to offer Ryanair anythink special to go onto an already busy route?
What relation do IB and AENA have opposed to BA and BAA for example? If they are owned by the same companies then fair enough but I don't think they are. The Spanish aren't German (
FT.com / UK - Germany forces up Emirates fares) - I doubt they want to protect their national carrier more than their own business.